basic action

If you use named capture with a regular expression (a person with a conditional expression on the left side ). A value is assigned to a local variable.

 /a (?<month>July)/ =~ 'Ruby is a July birth stone' month # => "July"

problem

However. Using variables in match conditions does not create local variables.

 a = 'a' /#{a} (?<month>July)/ =~ 'Ruby is a July birth stone' # => 8 month #=> #<NameError: undefined local variable or method `month' for main:Object>

The match itself is successful. The variable month does not exist.

Solution

Even in the same way. #match can capture normally by using the #match method.

 a = 'a' 'Ruby is a July birth stone'.match(/#{a} (?<month>July)/) { |matched| matched[:month] } # => July

How nice!

However, in the case of #match . Local variable month can not be created. If you really want to make it, you should assign it to the return value.

 a = 'a' month = 'Ruby is a July birth stone'.match(/#{a} (?<month>July)/) { |matched| matched[:month] } month # => "July"

Note

There is also a problem with the #match method. It is fine if it is the above writing method. Be careful if you use capture results in other ways.

Ruby | We cope with NoMethodError when it does not match in regular expression capture

environment

Ruby 2.2.4

Original by

Ruby | 正規表現の条件式に変数を使うと、名前付きキャプチャによる変数代入が出来ない

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